Cowitnessing & BUIS question

[CTGunner]

I'm going to pick up a S&W AR M&POR..it doesn't have any sights (front or rear) but it does have rail to mount BUIS. My question is how do I order BUIS that will line up with the Aimpoint Comp M2 that's going on (using a Larue Mount)?

http://www.budsgunshop.com/catalog/product_info.php/cPath/763/products_id/53496

 

[hardluk1]

Might try this at the ar forum?

 

[Barker45]

Call the guys at LaRue, they are awesome! Not only do they make some of the best gear but they are also fantastic to deal with.
As for a co-witness, you DO NOT want a true co-witness but rather a bottom 1/3 of the optic co-witness. That allows you to see your red dot clearly and in the very unlikely event that your aimpoint fails, you just lower you check-weld and use you BUIS. With this set up you can run your Ar with the BUIS up all the time.
The fellas at LaRue will put you on the right path. Their mounts are set-up to be bottom 1/3 co-witness.

 

[MrCleanOK]

The trick isn't ordering BUIS that will cowitness with your optics mount; it's ordering an optics mount that will cowitness with your BUIS. BUIS are all made to a standard height. It looks like that rifle has a receiver-height railed gas block. You should be able to get any BUIS you want (beware, Magpul advises against mounting their MBUS directly on a gas block). Troy is pretty much the standard for flip-ups. Midwest Industries has some good offerings for a little less money.

Larue mounts are top quality. You can't go wrong there. Also, there's nothing wrong with true or lower 1/3 cowitnessing. It's just a matter of preference. On a rifle with a fixed front sight, I prefer a true cowitness. On a rifle with flip-up sights, it truly doesn't matter if you'll be using the optic with the sights down.

 

[killchain]

This is off-topic, but please remember not to shoot 5.56mm out of that thing. That's a .223 Rem barrel, not a 5.56mm. It will cause problems.

Mentioning that because that topic comes up, ALOT. Now, back to topic...

I would recommend selecting a set of flip up sights, such as Troy or whatever, and then calling the guys at either Larue or Aimpoint and asking them if it will cowitness.

Also, you could compare some specifications. Find out how high the Aimpoint's glass is, figure out it's center, and then compare that to the set of BUIS you are wanting to try.

Hope this helps.

 

[AK103K]

I have an M&P that is similar to the one shown, but mine came with the free float, full railed handguard on it. It also came with what appear to be Troy BUIS on it. I also have an Aimpoint ML2 mounted on a LaRue M68 CCO cantilever mount. The BUIS do cowitness in the lower third of the tube.

I also have an Armalite M14A4(C) with GG&G BUIS and an Aimpoint M2 on one of GG&G's cantilever mounts. The BUIS cowitness more towards the center with that set up, and I actually prefer that more, as everything is regulated to the sights instead of the dot.

Either way, I prefer the irons down, and it offers a cleaner view, with no clutter. The sights can be up in a couple of seconds if need be.

Other than being annoying, it really doenst matter if anything is in the way, or if the front cover is closed, as long as you shoot with both eyes open.

Of the two, I do think the GG&G sights are the better sights. They are more solid and robust, and have little if any movement of the sight itself when up. The Troy's have a lot more play in them and I dont seem to shoot as well with them either.

I dont believe the specific model of GG&G front sight I have will work on the M&P though (height wise). The front rail on my Armalite appears to be lower than the rear rail. The M&P rails coincide, or, at least mine do, so I dont think they'd line up. This may be an issue with others too, so you may want to verify things before you buy.

This is off-topic, but please remember not to shoot 5.56mm out of that thing. That's a .223 Rem barrel, not a 5.56mm. It will cause problems.

Mine is marked 5.56 NATO 1/9.

I've shoot both out of both, and never had any issue. Same with .308/7.62.

 

[empeter]

This is off-topic, but please remember not to shoot 5.56mm out of that thing. That's a .223 Rem barrel, not a 5.56mm. It will cause problems.

If I remember correctly, and I do, all M&P-15's are 5.56, with possibly one exception. I know mine is, but it's a different model. But according to the S&W fact sheet, the M&P15OR definitely is.

http://www.smith-wesson.com/wcsstore/SmWesson/upload/other/ps/811003.pdf

When in doubt, consult the manual

 

[Balrog]

This is off-topic, but please remember not to shoot 5.56mm out of that thing. That's a .223 Rem barrel, not a 5.56mm. It will cause problems.

Mentioning that because that topic comes up, ALOT. Now, back to topic...

Thats completely wrong. There is no difference in a 223 barrel and a 5.56 barrel. It is the chambers that are different, not the barrels themselves, and the S&W is fine with 5.56 ammo.

 

[MrCleanOK]

Thats completely wrong. There is no difference in a 223 barrel and a 5.56 barrel. It is the chambers that are different, not the barrels themselves

Last time I checked, chambers were pretty integral parts of barrels on everything but revolvers and muzzle loaders.

 

[Balrog]

Last time I checked, chambers were pretty integral parts of barrels on everything but revolvers and muzzle loaders.

Yep you are correct, but it is the actual chamber size that is different, not bore size. The part that I was referring to that was completely wrong was the statement that you could not fire 5.56 ammo out of a S&W.

 

[HKGuns]

That is great, but your post, if someone just glosses over it will think they can shoot 5.56 out of a .223 barrel. You're splitting hairs and someone could get hurt by your saying "That's completely wrong". It isn't completely wrong.

 

[rbernie]

If y'all wanna discuss AR chamberings instead of BUIS, why not start a new thread instead of taking over somebody else's? Hijacking a thread is really not particularly on The High Road, no matter how honorable the intentions...

My question is how do I order BUIS that will line up with the Aimpoint Comp M2 that's going on

See post #4. I prefer a true co-witness, and choose my mountings based upon that. I find that it's best for me to groove the same cheekweld every time by having the irons and the Aimpoint reflect the same POA - YMMV.

Oh, and yes - Larue mounts are top notch stuff, if they give you the co-witness that you want.

 

[Balrog]

That is great, but your post, if someone just glosses over it will think they can shoot 5.56 out of a .223 barrel. You're splitting hairs and someone could get hurt by your saying "That's completely wrong". It isn't completely wrong.

Well whatever I guess. You can fire all the 5.56 ammo you want out of a 223 barrel. Its the chamber thats the problem. I think most people understand the difference between the barrel and the chamber.

Sorry about the hijacking...